U.S. patent application number 11/447772 was filed with the patent office on 2006-12-07 for optical element and optical pickup.
This patent application is currently assigned to KONICA MINOLTA HOLDINGS, INC.. Invention is credited to Satoru Hirose.
Application Number | 20060273284 11/447772 |
Document ID | / |
Family ID | 37493260 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060273284 |
Kind Code |
A1 |
Hirose; Satoru |
December 7, 2006 |
Optical element and optical pickup
Abstract
On one side of a liquid crystal layer, a first electrode is
provided, and, on the other side of the liquid crystal layer, a
second electrode, composed of a plurality of individual electrodes,
and a third electrode are provided. The second and third electrodes
have holes that are increasingly small away from the liquid crystal
layer. When the potential at the third electrode is set equal to or
lower than the potential at the second electrode, the liquid
crystal layer acts as a convex lens; when the potential at the
third electrode is set higher than the potential at the second
electrode, the liquid crystal layer acts as a concave lens. The
range in which the focal length can be varied depends on the
diameters of the holes, and giving the holes of the different
electrodes varying diameters helps widen the range. Moreover,
conductors can be laid to reach the electrodes at the outer edges
thereof so as not to directly face the liquid crystal layer. This
helps eliminate the influence of the conductors on the electric
field distribution in the liquid crystal layer.
Inventors: |
Hirose; Satoru; (Sakai-shi,
JP) |
Correspondence
Address: |
SIDLEY AUSTIN LLP
717 NORTH HARWOOD
SUITE 3400
DALLAS
TX
75201
US
|
Assignee: |
KONICA MINOLTA HOLDINGS,
INC.
|
Family ID: |
37493260 |
Appl. No.: |
11/447772 |
Filed: |
June 6, 2006 |
Current U.S.
Class: |
252/299.61 ;
G9B/7.119; G9B/7.13 |
Current CPC
Class: |
G02F 1/294 20210101;
G11B 7/1369 20130101; G02F 1/134309 20130101; G11B 7/13925
20130101; G02B 3/14 20130101 |
Class at
Publication: |
252/299.61 |
International
Class: |
C09K 19/34 20060101
C09K019/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2005 |
JP |
2005-166563 |
Dec 8, 2005 |
JP |
2005-354449 |
Claims
1. An optical element comprising: a liquid crystal layer; a first
transparent substrate arranged on one side of the liquid crystal
layer; a first electrode transparent and arranged on said one side
of the liquid crystal layer; a second transparent substrate
arranged on another side of the liquid crystal layer; a second
electrode arranged on said another side of the liquid crystal layer
and including a plurality of individual electrodes having holes; a
third electrode arranged on a side of the second electrode facing
away from the liquid crystal layer; an insulating layer laid
between the individual electrodes and the third electrode; and a
voltage applier for applying voltages between the first electrode
and the second and third electrodes, wherein the holes of the
individual electrodes are increasingly small away from the liquid
crystal layer.
2. The optical element of claim 1, wherein when viewed from a
perspective perpendicular to the liquid crystal layer, rims of the
holes of the individual electrodes do not overlap one another, an
exterior diameter of each of the individual electrodes except the
individual electrode closest to the liquid crystal layer is larger
than a diameter of the hole of the individual electrode located
adjacently on a liquid crystal layer side thereof, and an exterior
diameter of the third electrode is larger than a diameter of the
hole of the individual electrode located adjacent thereto.
3. The optical element of claim 2, wherein the second electrode
includes transparent individual electrodes and non-transparent
individual electrodes.
4. The optical element of claim 1, wherein the third electrode has
a hole of which a diameter is smaller than a diameter of, of the
holes of the individual electrodes, the smallest hole, and when
viewed from a perspective perpendicular to the liquid crystal
layer, a rim of the hole of the third electrode does not overlap
any of rims of the holes of the second electrode.
5. The optical element of claim 4, wherein the third electrode is
non-transparent.
6. The optical element of claim 4, wherein when viewed from a
perspective perpendicular to the liquid crystal layer, the holes of
the individual electrodes of the second electrode and the hole of
the third electrode describe concentric circles.
7. The optical element of claim 1, wherein the third electrode is
transparent and holeless.
8. The optical element of claim 1, wherein the second transparent
substrate is arranged between the liquid crystal layer and the
second electrode.
9. The optical element of claim 8, wherein part of a top surface of
the third electrode is carved out, starting from near an outer edge
thereof, so as to expose part of each of the individual electrodes
of the second electrode.
10. The optical element of claim 1, wherein the second transparent
substrate is arranged on a side of the third electrode facing away
from the liquid crystal layer.
11. The optical element of claim 1, wherein the voltage applier
applies the voltages between the first electrode and the second and
third electrodes such that a potential at the third electrode is
equal to or lower than a potential at the second electrode.
12. The optical element of claim 1, wherein the voltage applier
applies the voltages between the first electrode and the second and
third electrodes such that a potential at the third electrode is
higher than a potential at the second electrode.
13. The optical element of claim 1, wherein the first and second
transparent substrates are each a flat plate.
14. An optical element comprising: a liquid crystal layer; a first
transparent substrate arranged on one side of the liquid crystal
layer; a first electrode transparent and arranged on said one side
of the liquid crystal layer; a second transparent substrate
arranged on another side of the liquid crystal layer; a second
electrode arranged on said another side of the liquid crystal layer
and including one or more individual electrodes having holes; a
third electrode arranged on a side of the second electrode facing
away from the liquid crystal layer; an insulating layer arranged
between the individual electrodes and the third electrode; and a
voltage applier for applying voltages between the first electrode
and the second and third electrodes, wherein, of the individual
electrodes of the second electrode, the individual electrode
closest to the liquid crystal layer has a transparent part within
an optical path, and is so formed as to be continuous within the
optical path and to have a hole within the optical path.
15. The optical element of claim 14, wherein the second electrode
includes two or more of the individual electrodes, and the holes of
the individual electrodes are increasingly small away from the
liquid crystal layer.
16. An optical element comprising: a liquid crystal layer; a first
transparent substrate arranged on one side of the liquid crystal
layer; a first electrode arranged on said one side of the liquid
crystal layer and including a plurality of individual electrodes
having holes; a second electrode arranged on a side of the first
electrode facing away from the liquid crystal layer; a first
insulating layer for insulating the individual electrodes of the
first electrode from the second electrode; a second transparent
substrate arranged on another side of the liquid crystal layer; a
third electrode arranged on said another side of the liquid crystal
layer and including a plurality of individual electrodes having
holes; a fourth electrode arranged on a side of the third electrode
facing away from the liquid crystal layer; a second insulating
layer for insulating the individual electrodes of the third
electrode from the fourth electrode; and a voltage applier for
applying voltages between the first and second electrodes and the
third and fourth electrodes, wherein the holes of the individual
electrodes of the first electrode are increasingly small away from
the liquid crystal layer, and the holes of the individual
electrodes of the third electrode are increasingly small away from
the liquid crystal layer.
17. An optical element comprising: a liquid crystal layer;
transparent substrates arranged one on each side of the liquid
crystal layer; electrodes arranged one on each side of the liquid
crystal layer; and a voltage applier for applying voltages to the
electrodes to vary alignment of liquid crystal molecules in the
liquid crystal layer, wherein the electrode arranged on one side of
the liquid crystal layer is composed of a plurality of individual
electrodes that are laid on one another with an insulating layer
laid in between, and of the individual electrodes, the individual
electrode closest to the liquid crystal layer has a transparent
part within an optical path, and is so formed as to be continuous
within the optical path and to have a hole within the optical
path.
18. The optical element of claim 17, wherein the individual
electrodes are laid in three or more layers, of the individual
electrodes, the individual electrodes other than the individual
electrode farthest from the liquid crystal layer are so formed as
to be continuous within the optical path and to have holes within
the optical path, and the holes of said other individual electrodes
are formed increasingly small away from the liquid crystal
layer.
19. The optical element of claim 17, wherein the hole of the
individual electrode closest to the liquid crystal layer is formed
in a position corresponding to a peak of coma.
20. The optical element of claim 19, wherein the individual
electrodes are laid in three or more layers, of the individual
electrodes, the individual electrode in a second layer away from
the liquid crystal layer is so formed as to be continuous within
the optical path and to have a hole within the optical path; the
hole of the individual electrode in the second layer away from the
liquid crystal layer is formed in a position corresponding to a
peak of coma, and the hole of the individual electrode in the
second layer away from the liquid crystal layer is formed smaller
than the hole of the individual electrode closest to the liquid
crystal layer.
21. The optical element of claim 17, wherein of the individual
electrodes, the individual electrode farthest from the liquid
crystal layer is so formed as to cover the holes of the other
individual electrodes.
22. The optical element of claim 21, wherein the individual
electrode farthest from the liquid crystal layer is composed of a
plurality of electrode segments laid in a same layer.
23. The optical element of claim 22, wherein the individual
electrode farthest from the liquid crystal layer is composed of as
many electrode segments as there are holes in the individual
electrode adjacent thereto.
24. The optical element of claim 22, wherein the electrode segments
include an electrode segment to which, despite in the same layer as
the other electrode segments, a voltage different from a voltage
applied to the other electrode segments is applied.
25. The optical element of claim 17, wherein the individual
electrodes are formed on a side, facing away from the liquid
crystal layer, of the transparent substrate arranged on said one
side of the liquid crystal layer.
26. The optical element of claim 17, wherein the individual
electrodes are formed on a side, facing toward the liquid crystal
layer, of the transparent substrate arranged on said one side the
liquid crystal layer, with an insulating layer laid between the
individual electrodes and the liquid crystal layer.
27. The optical element of claim 17, wherein an electrode pattern
on another side of the liquid crystal layer and an electrode
pattern on said one side of the liquid crystal layer are symmetric
with each other about the liquid crystal layer.
28. The optical element of claim 17, wherein the electrode on
another side of the liquid crystal layer is composed of a plurality
of individual electrodes that are laid on one another with an
insulating layer laid in between and that have holes, the holes of
the individual electrodes are formed increasingly small away from
the liquid crystal layer so that, when viewed from a perspective
perpendicular to the liquid crystal layer, rims of the holes of the
individual electrodes do not overlap one another.
29. The optical element of claim 28, wherein of every two of the
individual electrodes adjacent to each other across the insulating
layer laid in between, the individual electrode farther from the
liquid crystal layer has a larger exterior diameter than the
diameter of the hole of the individual electrode closer to the
liquid crystal layer.
30. An optical pickup comprising: an optical element, the optical
element comprising: a liquid crystal layer; a first transparent
substrate arranged on one side of the liquid crystal layer; a first
electrode transparent and arranged on said one side of the liquid
crystal layer; a second transparent substrate arranged on another
side of the liquid crystal layer; a second electrode arranged on
said another side of the liquid crystal layer and including a
plurality of individual electrodes having holes; a third electrode
arranged on a side of the second electrode facing away from the
liquid crystal layer; an insulating layer laid between the
individual electrodes and the third electrode; and a voltage
applier for applying voltages between the first electrode and the
second and third electrodes, wherein the holes of the individual
electrodes are increasingly small away from the liquid crystal
layer.
31. An optical pickup comprising: an optical element, the optical
element comprising: a liquid crystal layer; transparent substrates
arranged one on each side of the liquid crystal layer; electrodes
arranged one on each side of the liquid crystal layer; and a
voltage applier for applying voltages to the electrodes to vary
alignment of liquid crystal molecules in the liquid crystal layer,
wherein the electrode arranged on one side of the liquid crystal
layer is composed of a plurality of individual electrodes that are
laid on one another with an insulating layer laid in between, and
of the individual electrodes, the individual electrode closest to
the liquid crystal layer has a transparent part within an optical
path, and is so formed as to be continuous within the optical path
and to have a hole within the optical path.
Description
[0001] This application is based on Japanese Patent Application No.
2005-166563 filed on Jun. 7, 2005 and Japanese Patent Application
No. 2005-354449 filed on Dec. 8, 2005, the contents of both of
which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical element using a
liquid crystal, and to an optical pickup incorporating such an
optical element.
[0004] 2. Description of Related Art
[0005] A liquid crystal that has dielectric constant anisotropy
exhibits electric field dependence; that is, it varies its
molecular alignment according to the directions of electric force
lines. Thus, as the electric field is controlled, the optical
characteristics of the liquid crystal can be controlled. This has
led to proposals of various optical elements using liquid
crystals.
[0006] Patent Document 1, listed below, proposes a variable-focus
optical system wherein, as shown in FIG. 28, ring-shaped electrodes
101 are arranged concentrically in a pattern of a Fresnel zone
plate. This makes it possible to produce, on a liquid crystal
panel, a pattern of a Fresnel zone plate of which the spatial
frequency can be controlled electrically.
[0007] Non-patent Document 1, listed below, discloses an optical
element that can vary its focal length by so controlling a voltage
as to vary the refractive index distribution of a liquid crystal
arranged between electrodes having openings.
[0008] Non-patent Document 2, listed below, proposses a liquid
crystal lens that is built as a convex lens (having a positive
focal length) or concave lens (having a negative focal length)
having a liquid crystal sealed between a plano-convex lens or
plano-concave lens and a flat-plate glass substrate. In this liquid
crystal lens, as the electric field distribution in its liquid
crystal portion is controlled, its focal length can be varied in a
positive or negative range.
[0009] Patent Documents 2 to 4, listed below, disclose optical
elements that permit correction of coma. Specifically, Patent
Document 2 proposes an optical element wherein, in positions
corresponding to openings formed in pattern electrodes (positions
deviated from the openings along the optical axis), transparent
electrode layers are laid in separate layers from the pattern
electrodes. This structure helps eliminate the influence of the
potential varying abruptly at the openings in the pattern
electrodes, and thus helps enhance the accuracy of aberration
correction.
[0010] Patent Document 3 proposes an optical element wherein, in
openings formed in a transparent electrode, a transparent
high-resistance film is laid so that the transparent electrode has
apparently no openings at all. This structure helps prevent
diffraction of light that occurs between different parts of the
transparent electrode, and thus helps obtain a satisfactory optical
signal. That is, with no openings in the transparent electrode,
there is no place where the potential is locally equal to the
reference potential (O V), nor does diffraction of light occur;
thus the loss of light can be minimized.
[0011] Patent Document 4 proposes wavefront aberration correcting
means and an optical pickup that involve electrodes divided into a
shape corresponding to the wavefront aberration distribution
attributable to the tilt angle of an optical disc. With this
structure, even when the optical disc tilts during reproduction
from it, the light spot formed on the recording surface of the
optical disc can be so corrected that the magnitude of the
wavefront aberration attributable to the tilt is suppressed within
a predetermined rage. This ensures satisfactory reproduction.
[0012] The patent and non-patent documents mentioned above are as
follows: [0013] Patent Document 1: JP-A-S63-249125 (pp. 156 and
157, and FIG. 5) [0014] Non-patent Document 1: Jpn. J. Appl. Phys.,
Vol. 41, No. 5, p. L571 [0015] Non-patent Document 2: Jpn. J. Appl.
Phys., Vol. 18, pp. 1679 and 1979 [0016] Patent Document 2:
JP-A-2001-176108 [0017] Patent Document 3: JP-A-2004-334028 [0018]
Patent Document 4: JP-B-3538520
[0019] The conventional structures described above, however, have
the following disadvantages. In the variable-focus optical system
according to Patent Document 1, the ring-shaped electrodes 101 have
parts of them cut apart (made discontinuous) to leave a space for
laying conductors 102 for applying voltages to the electrodes 101.
As a result, the electric field distribution in the liquid crystal
portion is influenced by the area where the electrodes are cut
apart and by the conductors. This causes the pattern of the Fresnel
zone plate that is produced on the liquid crystal panel to be
deformed from the ideal concentric shape, and may thus lead to
degraded optical characteristics.
[0020] In the optical element according to Non-patent Document 1,
the range in which the focal length can be varied depends largely
on the diameter of the openings in the electrodes and on the
distance between the electrodes. This results in the focal length
being variable only in a range narrower than is expected. With the
optical element according to Non-patent Document 2, the focal
length can be varied, indeed, but only in a positive range when a
plano-convex lens is used and only in a negative range when a
plano-concave lens is used.
[0021] In any of the optical elements according to Patent Documents
2 to 4, which can correct coma, the electrodes are laid wherever
aberration needs to be corrected. Thus, the electrodes are laid in
insular segments where coma has peaks. Accordingly, conductors for
applying voltages to the electrodes in insular segments need to be
laid to cross the optical path. Consequently, the electric field
distribution produced by the electrodes is influenced by the
conductors.
[0022] Thus, in the structure of any of the optical elements
according to Patent Documents 1 to 4, the conductors leading to the
electrodes are located in the optical path. Disadvantageously, this
degrades the characteristics of these optical elements.
SUMMARY OF THE INVENTION
[0023] In view of the conventionally experienced disadvantages
discussed above, it is an object of the present invention to
provide an optical element using a liquid crystal, and also an
optical pickup incorporating it, wherein an electrode (for example,
a ring-shaped electrode) having an opening has no part of it cut
apart (made discontinuous), so that the electric field distribution
produced by the electrode is not influenced by a conductor. It is
another object of the present invention to provide an optical
element, and also an optical pickup incorporating it, of which the
focal length can be varied over a wide range encompassing both
positive and negative focal lengths.
[0024] To achieve the above object, according to one aspect of the
present invention, an optical element is provided with: a liquid
crystal layer; a first transparent substrate arranged on one side
of the liquid crystal layer; a first electrode transparent and
arranged on the one side of the liquid crystal layer; a second
transparent substrate arranged on the other side of the liquid
crystal layer; a second electrode arranged on the other side of the
liquid crystal layer and including a plurality of individual
electrodes having holes; a third electrode arranged on the side of
the second electrode facing away from the liquid crystal layer; an
insulating layer laid between the individual electrodes and the
third electrode; and a voltage applier for applying voltages
between the first electrode and the second and third electrodes.
Here, the holes of the individual electrodes are increasingly small
away from the liquid crystal layer.
[0025] In this structure, voltages are applied between, on one
hand, the first electrode and, on the other hand, the second
electrode, which is composed of a plurality of individual
electrodes having holes, and the third electrode. This produces an
electric field, which re-aligns the liquid crystal molecules in the
liquid crystal layer and thereby varies the refractive index
distribution of the liquid crystal layer. Thus, the optical element
according to this aspect of the present invention acts as a lens of
which the focal length can be varied in a range encompassing
positive and negative focal lengths. Moreover, since the second and
third electrodes are laid on each other, conductors can be fitted
thereto without forming cuts in those electrodes. This helps
produce an ideal electric field distribution.
[0026] Moreover, building the second electrode with a plurality of
individual electrodes having holes with varying diameters helps
widen the range in which the focal length can be varied.
Furthermore, forming the holes of the individual electrodes
increasingly small away from the liquid crystal layer makes it
possible to control the electric field distribution finely.
[0027] Of the individual electrodes, the one closest to the liquid
crystal layer may have a transparent part within the optical path.
This helps avoid a lowering in the transmissivity of the individual
electrode closest to the liquid crystal layer to the light
transmitted therethrough.
[0028] According to another aspect of the present invention, an
optical element is provided with: a liquid crystal layer; a first
transparent substrate arranged on one side of the liquid crystal
layer; a first electrode transparent and arranged on the one side
of the liquid crystal layer; a second transparent substrate
arranged on the other side of the liquid crystal layer; a second
electrode arranged on the other side of the liquid crystal layer
and including one or more individual electrodes having holes; a
third electrode arranged on the side of the second electrode facing
away from the liquid crystal layer; an insulating layer arranged
between the individual electrodes and the third electrode; and a
voltage applier for applying voltages between the first electrode
and the second and third electrodes. Here, of the individual
electrodes of the second electrode, the one closest to the liquid
crystal layer has a transparent part within the optical path, and
is so formed as to be continuous within the optical path and to
have a hole within the optical path.
[0029] In this structure, voltages are applied between, on one
hand, the first electrode and, on the other hand, the second
electrode, which includes one or more individual electrodes having
holes, and the third electrode. This produces an electric field,
which re-aligns the liquid crystal molecules in the liquid crystal
layer and thereby varies the refractive index distribution of the
liquid crystal layer. Thus, the optical element according to this
aspect of the present invention acts as a lens of which the focal
length can be varied in a range encompassing positive and negative
focal lengths. Moreover, since the second and third electrodes are
laid on each other, conductors can be fitted thereto without
forming cuts in those electrodes. This helps produce an ideal
electric field distribution.
[0030] In particular, of the individual electrodes of the second
electrode, the one closest to the liquid crystal layer is so formed
as to be continuous within the optical path. Thus, simply by
forming this individual electrode so that a part thereof protrudes
out of the optical path, it is possible to provide, outside the
optical path, a conductor for applying a voltage to that individual
electrode so that the voltage can be applied to the entire
individual electrode. Thus, in this case, there is no need to
provide the conductor within the optical path. This also helps
eliminate the influence of the conductor on the electric field
distribution, and helps produce an ideal electric field
distribution. As a result, it is possible to avoid degradation of
the characteristics of the optical element attributable to the
conductor.
[0031] Moreover, the above-mentioned individual electrode has a
hole within the optical path, and thus, by varying the electric
field distribution according to where to form the hole, it is
possible to correct various kinds of aberration. Furthermore, the
above-mentioned individual electrode has a transparent part within
the optical path. This helps avoid a lowering in the transmissivity
of the individual electrode to the light transmitted
therethrough.
[0032] According to another aspect of the present invention, an
optical element is provided with: a liquid crystal layer; a first
transparent substrate arranged on one side of the liquid crystal
layer; a first electrode arranged on the one side of the liquid
crystal layer and including a plurality of individual electrodes
having holes; a second electrode arranged on the side of the first
electrode facing away from the liquid crystal layer; a first
insulating layer for insulating the individual electrodes of the
first electrode from the second electrode; a second transparent
substrate arranged on the other side of the liquid crystal layer; a
third electrode arranged on the other side of the liquid crystal
layer and including a plurality of individual electrodes having
holes; a fourth electrode arranged on the side of the third
electrode facing away from the liquid crystal layer; a second
insulating layer for insulating the individual electrodes of the
third electrode from the fourth electrode; and a voltage applier
for applying voltages between the first and second electrodes and
the third and fourth electrodes. Here, the holes of the individual
electrodes of the first electrode are increasingly small away from
the liquid crystal layer, and the holes of the individual
electrodes of the third electrode are increasingly small away from
the liquid crystal layer.
[0033] By arranging the first and second electrodes on one side of
the liquid crystal layer and the third and fourth electrodes on the
other in this way, it is possible to control the electric field
distribution of the optical element more finely, and thereby to
enhance the accuracy with which the liquid crystal layer acts as a
lens or the like.
[0034] According to another aspect of the present invention, an
optical element is provided with: a liquid crystal layer;
transparent substrates arranged one on each side of the liquid
crystal layer; electrodes arranged one on each side of the liquid
crystal layer; and a voltage applier for applying voltages to the
electrodes to vary the alignment of the liquid crystal molecules in
the liquid crystal layer. Here, the electrode arranged on one side
of the liquid crystal layer is composed of a plurality of
individual electrodes that are laid on one another with an
insulating layer laid in between, and, of the individual
electrodes, the one closest to the liquid crystal layer has a
transparent part within the optical path, and is so formed as to be
continuous within the optical path and to have a hole within the
optical path.
[0035] In this structure, of the individual electrodes formed on
one side of the liquid crystal layer, the one closest to the liquid
crystal layer is so formed as to be continuous within the optical
path. Thus, simply by forming this individual electrode so that a
part thereof protrudes out of the optical path, it is possible to
provide, outside the optical path, a conductor for applying a
voltage to that individual electrode so that the voltage can be
applied to the entire individual electrode. Thus, in this case,
there is no need to provide the conductor within the optical path.
This helps eliminate the influence of the conductor on the electric
field distribution, and helps produce an ideal electric field
distribution. As a result, it is possible to avoid degradation of
the characteristics of the optical element attributable to the
conductor.
[0036] Moreover, the above-mentioned individual electrode has a
hole within the optical path, and thus, by varying the electric
field distribution according to where to form the hole, it is
possible to correct various kinds of aberration. Specifically, for
example, forming the hole so that the center thereof coincides with
the optical axis makes it possible to correct spherical aberration;
forming the hole in a position corresponding to a peak of coma
makes it possible to correct coma.
[0037] Moreover, the above-mentioned individual electrode has a
transparent part within the optical path. This helps avoid a
lowering in the transmissivity of the individual electrode to the
light transmitted therethrough.
[0038] According to still another aspect of the present invention,
an optical pickup is provided with an optical element, like one of
those described above, according to the present invention. Since an
optical element according to the present invention helps avoid
degradation of characteristics resulting from disturbance in an
electric field distribution attributable to conductors,
incorporating one in an optical pickup helps enhance the accuracy
with which information is recorded to and reproduced from an
optical recording medium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The above and other objects and features of the present
invention will become clear through the following description of
preferred embodiments taken in conjunction with the accompanying
drawings, in which:
[0040] FIG. 1 is a plan view of the optical element of a first
embodiment of the present invention;
[0041] FIG. 2 is a cross-sectional view along line A-A' shown in
FIG. 1 as viewed in the arrow-indicated direction;
[0042] FIG. 3 is a diagram showing a cross section of a liquid
crystal layer along with the electric force lines produced when the
potential at a third electrode is set equal to the potential at a
second electrode;
[0043] FIG. 4 is a diagram showing a cross section of a liquid
crystal layer along with the electric force lines produced when the
potential at a third electrode is set lower than the potential at a
second electrode;
[0044] FIG. 5 is a plan view of the optical element of the first
embodiment, in a case where contacts to individual electrodes are
so provided as to be accessible from the top surface of a third
electrode;
[0045] FIG. 6 is a plan view of the optical element of the first
embodiment, in a case where individual electrodes and a third
electrodes are made increasingly smaller away from a liquid crystal
layer and where conductors overlap one another;
[0046] FIG. 7 is a cross-sectional view along line B-B' shown in
FIG. 6 as viewed in the arrow-indicated direction;
[0047] FIG. 8 is a plan view of the optical element of the first
embodiment, in a case where individual electrodes and a third
electrodes are made increasingly smaller away from a liquid crystal
layer and where conductors do not overlap one another;
[0048] FIG. 9 is a cross-sectional view of the optical element of
the first embodiment, in a case where a third electrode without a
hole is provided;
[0049] FIG. 10 is a cross-sectional view of the optical element of
the first embodiment, in a case where a second transparent
substrate is provided outside a third electrode;
[0050] FIG. 11 is a cross-sectional view of the optical element of
a second embodiment of the invention;
[0051] FIG. 12 is a diagram illustrating an outline of the
construction of an optical pickup to which the optical element of
each embodiment is applicable;
[0052] FIG. 13A is a plan view showing an outline of the structure
of the optical element of a third embodiment of the present
invention;
[0053] FIG. 13B is a cross-sectional view along line C-C' shown in
FIG. 13A as viewed in the arrow-indicated direction;
[0054] FIG. 14A is a plan view showing an outline of the structure
of the individual electrode closest to a liquid crystal layer in
the optical element;
[0055] FIG. 14B is a plan view showing an outline of the structure
of the individual electrode farthest from a liquid crystal layer in
the optical element
[0056] FIG. 15 is a diagram illustrating the voltages applied to
different electrodes of the optical element, the phase of the light
transmitted through the liquid crystal layer thereof, and the coma
observed;
[0057] FIG. 16A is a plan view showing an outline of the structure
of the optical element of a fourth embodiment of the present
invention;
[0058] FIG. 16B is a cross-sectional view along line D-D' shown in
FIG. 16A as viewed in the arrow-indicated direction;
[0059] FIG. 17 is a plan view showing an outline of the structure
of the second individual electrode as counted from a liquid crystal
layer in the optical element;
[0060] FIG. 18 is a diagram illustrating the phase of the light
transmitted through the liquid crystal layer of the optical element
and the coma observed;
[0061] FIG. 19A is a plan view showing an outline of the structure
of the optical element of a fifth embodiment of the present
invention;
[0062] FIG. 19B is a cross-sectional view along line E-E' shown in
FIG. 19A as viewed in the arrow-indicated direction;
[0063] FIG. 20 is a diagram illustrating the phase of the light
transmitted through the liquid crystal layer of the optical element
and the coma observed;
[0064] FIG. 21 is a cross-sectional view showing another example of
the structure of the optical element;
[0065] FIG. 22A is a plan view showing an outline of the structure
of the optical element of a sixth embodiment of the present
invention;
[0066] FIG. 22B is a cross-sectional view along line F-F' shown in
FIG. 22A as viewed in the arrow-indicated direction;
[0067] FIG. 23A is a plan view showing an outline of the structure
of the optical element of a seventh embodiment of the present
invention;
[0068] FIG. 23B is a cross-sectional view along line G-G' shown in
FIG. 23A as viewed in the arrow-indicated direction;
[0069] FIG. 24A is a plan view showing an outline of the structure
of the optical element of an eighth embodiment of the present
invention;
[0070] FIG. 24B is a cross-sectional view along line H-H' shown in
FIG. 24A as viewed in the arrow-indicated direction;
[0071] FIG. 25 is a plan view showing an outline of the structure
of the individual electrode farthest from a liquid crystal layer in
the optical element;
[0072] FIG. 26 is a diagram illustrating the phase of the light
transmitted through the liquid crystal layer of the optical element
and the coma observed;
[0073] FIG. 27 is a plan view showing another example of the
structure of the optical element of the first embodiment; and
[0074] FIG. 28 is a plan view of electrodes in a conventional
optical element.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First Embodiment
[0075] A first embodiment of the present invention will be
described below with reference to the relevant drawings. FIG. 1 is
a plan view of the optical element of the first embodiment, and
FIG. 2 is a cross-sectional view thereof alone line A-A' shown in
FIG. 1 as viewed in the arrow-indicated direction.
[0076] First, the structure of the optical element 10 will be
described. As shown in FIGS. 1 and 2, in the optical element 10, a
first transparent substrate 11 and a second transparent substrate
12 that have equal exterior diameters and are circular in shape are
arranged to face each other at a distance from each other, with a
liquid crystal layer 13 sealed in between. Over the entire surface
of the first transparent substrate 11 facing toward the liquid
crystal layer 13, a first electrode 14 that is transparent is
laid.
[0077] On the surface of the second transparent substrate 12 facing
away from the liquid crystal layer 13, a second electrode 20 is
laid. The second electrode 20 is composed of a plurality of
individual electrodes 21a to 21e that are transparent. The
individual electrodes 21a to 21e have the same exterior diameter as
the second transparent substrate 12, have circular holes 27 one
each, and are separated from one another with insulating layers 28.
The holes of the individual electrodes 21a to 21e are increasingly
large toward the liquid crystal layer 13, and, when viewed from a
perspective perpendicular to the liquid crystal layer 13, the
individual electrodes 21a to 21e have the centers thereof at the
same point, describing concentric circles.
[0078] On the surface of the second electrode 20 facing away from
the liquid crystal layer 13, a third electrode 26 that is
transparent is laid. The third electrode 26 is separated from the
second electrode 20 with an insulating layer 28, has the same
exterior diameter as the second electrode 20, and has a hole 27
smaller than the smallest among the holes 27 of the second
electrode 20, that is, smaller than the hole 27 of the individual
electrode 21e. Here, when viewed from a perspective perpendicular
to the liquid crystal layer 13, the hole 27 of the third electrode
26 also describes a circle concentric with those described by the
holes 27 of the second electrode 20.
[0079] The first transparent substrate 11 and the second
transparent substrate 12 are each formed as a transparent
insulating member formed of, for example, glass or resin. The first
electrode 14, the second electrode 20, and the third electrode 26
are each formed of an electrically conductive, optically
transmissive substance such as indium tin oxide (ITO).
[0080] To the optical element 10, voltage applying means 30 (a
voltage applier) is connected. From the outer edge of each
electrode, a conductor 31 formed of conductive metal wire runs to
the voltage applying means 30. The voltage applying means 30
applies in-phase alternating-current voltages between the first
electrode 14 and the second and third electrodes 20 and 26. The
voltages applied by the voltage applying means 30 may be
direct-current voltages.
[0081] In the structure described above, the individual electrodes
21a to 21e of the second electrode 20 and the third electrode 26
each have the shape of a continuous ring without a cut. Moreover,
when viewed from a perspective perpendicular to the liquid crystal
layer 13, the second electrode 20 and the third electrode 26 leave
no gap among them. Thus, the conductors 31 do not directly face the
liquid crystal layer 13, and hence do not influence the electric
field produced when voltages are applied between the first
electrode 14 and the second and third electrodes 20 and 26. This
makes it possible to produce a disturbance-free electric field that
is axisymmetric about the center axis through the holes 27.
[0082] Next, a description will be given of the voltage control in
the optical element 10. When the voltage applying means 30 applies
voltages between the first electrode 14 and the second and third
electrodes 20 and 26 so that the potentials at the second electrode
20 and at the third electrode 26 are equal relative to the
potential at the first electrode 14, there is produced, between the
first electrode 14 and the second and third electrodes 20 and 26,
an electric field distribution similar to one produced when the
second electrode 20 is non-existent, that is, when only the third
electrode 26 exists. The reason is that, in comparison with the
second transparent substrate 12, the second electrode 20 and the
third electrode 26 including the insulating layers 28 are so thin
that the distances from the first electrode 14 to each of the
individual electrodes 21a to 21e of the second electrode 20 and to
the third electrode 26 can be regarded as uniform.
[0083] FIG. 3 shows the electric force lines 16 observed in this
state. The electric force lines 16 describe curves that approach a
central part of the optical element 10 as they run from the second
electrode 20 side toward the first electrode 14. The electric force
lines 16 re-align the liquid crystal molecules 13a in the liquid
crystal layer 13 in such a way that the liquid crystal layer 13
exhibits increasingly high refractive indices toward the center
axis through the holes 27. This makes the optical element 10 act as
a convex lens. Here, by controlling the voltages to the second
electrode 20 and the third electrode 26, it is possible to control
the refractive index distribution, and thereby it is possible to
control the focal length of the optical element 10 within a range
restricted by the size of the hole 27 of the third electrode
26.
[0084] When the voltages are independently controlled such that the
entire second electrode 20 is set at the same potential and the
third electrode 26 is set at a potential lower than that at the
second electrode 20, it is possible to produce an electric field
distribution similar to one produced when, of the individual
electrodes of the second electrode 20, only the one 21e closest to
the third electrode 26 exists.
[0085] Alternatively, when the voltages are independently
controlled such that the individual electrodes 21a to 21d of the
second electrode 20 are set at the same potential and that the
individual electrode 21e and the third electrode 26 are set at a
potential lower than the just-mentioned potential, it is possible
to produce an electric field distribution similar to one produced
when only the individual electrode 21d exits. In similar manners,
for each of the individual electrodes 21a to 21c, it is possible to
produce an electric field distribution similar to one produced when
it alone exits.
[0086] In any of these cases, the optical element 10 acts as a
convex lens, but, from one case to another, the size of the hole 27
of the electrode that is regarded as existing varies, and
accordingly the range in which the focal length can be varied
varies. Thus, the optical element 10 can vary the focal length
thereof in a wider range than when only one electrode having a hole
is arranged to face the first electrode 14 with the liquid crystal
layer 13 sandwiched in between (for example, when the second
electrode 20 is nonexistent and only the third electrode 26
exists).
[0087] Moreover, by independently controlling the potentials at the
second electrode 20 and at the third electrode 26, it is possible
to make the optical element 10 act as a convex lens having a
desired refractive index distribution. For example, by producing a
refractive index distribution such that the liquid crystal layer 13
have a uniform focal length in different parts thereof from the
center axis through the holes 27 to the edge, it is possible to
make the optical element 10 act as a convex lens with little
spherical aberration.
[0088] On the other hand, when the potential at the third electrode
26 is set higher than the potential at the second electrode 20, as
shown in FIG. 4, there are produced electric force lines 16 that
spread out toward an outer edge part of the optical element 10 as
they run from the second electrode 20 side toward the first
electrode 14. The electric force lines 16 re-align the liquid
crystal molecules 13a in the liquid crystal layer 13 in such a way
that the liquid crystal layer 13 exhibits increasingly low
refractive indices toward the center axis through the holes 27.
This makes the optical element 10 act as a concave lens. Also in
this case, by controlling the potentials at the different
electrodes in similar manners as with a convex lens, it is possible
to vary the focal length of the optical element 10. Here, by
properly controlling the potentials at the individual electrodes
21a to 21e of the second electrode 20 and at the third electrode
26, it is possible to make the optical element 10 act as a concave
lens having a desired refractive index distribution.
[0089] The description above deals with a case where the liquid
crystal molecules 13a are positively dielectric. By contrast, in a
case where they are negatively dielectric, setting the potential at
the third electrode 26 lower than the potential at the second
electrode 20 makes the optical element 10 act as a convex lens, and
setting the potential at the third electrode 26 higher than the
potential at the second electrode 20 makes the optical element 10
act as a concave lens.
[0090] Thus, with the structure described above, simply through
voltage control, the optical element 10 can be made to act both as
a convex lens and as a concave lens. That is, the optical element
10 acts as a lens of which the focal length can be varied over a
wide range encompassing both positive and negative focal lengths.
Moreover, as described above, the electric field distribution
produced across the liquid crystal layer 13 is free from
disturbance attributable to factors such as conductors, and
consequently the liquid crystal layer 13 exhibits a neat refractive
index distribution that is axisymmetric about the center axis
through the holes 27. Thus, the optical element 10 produces a
disturbance-free image.
[0091] As a modification, as shown in FIG. 5, contacts 22a to 22e
may be provided on the individual electrodes 21a to 21e,
respectively, by carving out outer edge parts of the third
electrode 26 so as to expose parts of the top surfaces of the
individual electrodes 21a to 21e, so that the conductors 31 leading
from the second electrode 20 and the third electrode 26 to the
voltage applying means 30 are connected to those contacts 22a to
22e. This makes easy the fitting of the conductors 31 to the
individual electrodes 21a to 21e. Incidentally, the top surface of
the third electrode 26 is exposed from the beginning, and therefore
any part thereof can be used as a contact, so that a conductor 31
is fitted thereto.
[0092] In the first embodiment, so long as, among the individual
electrodes 21a to 21e of the second electrode 20 and the third
electrode 26, the sizes of the holes thereof fulfill the
relationship described above, and in addition, among those
electrodes, the exterior diameter of each electrode is greater than
the diameter of the hole 27 of the one located adjacently on the
liquid crystal layer 13 side thereof, as shown in FIGS. 6 and 7,
the exterior diameters of the electrodes do not necessarily have to
be equal. FIG. 6 is a plan view of another example of the optical
element of the first embodiment, and FIG. 7 is a cross-sectional
view thereof along line B-B' shown in FIG. 6 as viewed in the
arrow-indicated direction. This structure is possible because, of
the second and third electrodes 20 and 26, the parts that do not
face the liquid crystal layer 13 contribute little to producing the
electric field distribution between the second transparent
substrate 12 and the second and third electrodes 20 and 26.
[0093] In this case, the conductors 31 are provided to run outward
from the outer edges of the electrodes. These conductors, too, do
not influence the electric field distribution between the first
electrode 14 and the second and third electrodes 20 and 26. The
reason is that, when viewed from a perspective perpendicular to the
liquid crystal layer 13, the second and third electrodes 20 and 26
leave no gap among them, and thus the conductors 31 do not directly
face the liquid crystal layer 13. FIG. 6 shows a case where the
conductors overlap one another, and FIG. 8 shows a case where the
conductors are displaced from one another. In either case, the
optical element 10 acts equally.
[0094] The conductors 31 may be formed integrally with, and hence
with the same material as, the second and third electrodes 20 and
26, or may be formed as conductors separate therefrom. FIGS. 6 to 8
deal with cases where the insulating layers 28 are not laid above
where the individual electrodes 21a to 21e do not overlap one
another; it is, however, also possible to lay the insulating layers
28 also above this no-overlap part.
[0095] In the first embodiment, as shown in FIG. 9, the third
electrode 26 may have no hole. This eliminates the need to adjust
the position of a hole in the third electrode 26 during the
fabrication of the optical element 10, and thus makes its
fabrication easier. Moreover, with no hole in the third electrode
26, the optical element 10 is less likely to be influenced by an
external electric field.
[0096] FIG. 1 deals with a case where the second electrode 20
includes five individual electrodes, and FIG. 9 deals with a case
where it includes six; it should be understood, however, that so
long as the second electrode 20 includes at least one individual
electrode, the optical element 10 can be made to act as described
above.
[0097] In the first embodiment, any of the individual electrodes
21a to 21e of the second electrode 20, or the third electrode 26
when it has a hole, may be formed of a non-transparent material
such as aluminum. In this case, the non-transparent electrode acts
as an aperture stop of the optical element 10 (serving to shield
light that would pass through the part of the liquid crystal layer
13 that is located away from the center axis through the holes 27
and that thus tends to produce spherical aberration). Thus, without
complicated voltage control, the optical element 10 can be made to
act as a lens with little spherical aberration.
[0098] In the first embodiment, the first and second transparent
substrates 11 and 12 may each be given flat surface, or may each be
built as a convex or concave lens. By using a convex or concave
lens as one or both of the first and second transparent substrates
11 and 12, it is possible to shift the range in which the focal
length can be varied in the positive or negative direction.
[0099] In FIG. 1, the second and third electrodes 20 and 26 are
arranged on the side of the second transparent substrate 12 facing
away from the liquid crystal layer 13; as shown in FIG. 10, they
may also be arranged on the side of the second transparent
substrate 12 facing toward the liquid crystal layer 13. In this
case, the distances from the first electrode 14 to the individual
electrodes 21a to 21e of the second electrode 20 and to the third
electrode 26 are shorter, and the electric force lines produced
across the liquid crystal layer 13 are perpendicular to each
electrode and are substantially parallel to one another. This
permits the electric field distribution produced in the liquid
crystal layer 13 to be controlled more independently for each of
the parts of the different electrodes facing the first electrode
14. This makes it possible to use the optical element 10 not only
as a convex or concave lens but also, by forming a clear concentric
pattern in the liquid crystal layer 13, as a diffraction grating
such as a Fresnel zone plate and for aberration correction in an
optical pickup such as one for DVDs.
[0100] It should be noted that, since the individual electrodes 21a
to 21e of the second electrode 20 are transparent, at least the
individual electrode 21a closest to the liquid crystal layer 13 can
be said to be an electrode having a transparent part within the
optical path. Making a part of the individual electrode 21a located
within the optical path transparent in this way helps avoid a
lowering in the transmissivity of the individual electrode 21a to
the light transmitted therethrough.
Second Embodiment
[0101] A second embodiment of the present invention will be
described below with reference to the relevant drawings. FIG. 11 is
a cross-sectional view of the optical element of the second
embodiment. The second embodiment differs from the first embodiment
in that, instead of the first electrode, a fourth electrode and a
fifth electrode are provided; in other respects, the second
embodiment is the same as the first embodiment, and therefore, in
FIG. 11, such parts that find substantially equivalent parts in the
first embodiment are identified by common reference numerals.
[0102] In the optical element 10 of the second embodiment, as shown
in FIG. 11, on the surface of the first transparent substrate 11
facing away from the liquid crystal layer 13, a fourth electrode 41
and a fifth electrode 42 are laid that have the same structures as
the second electrode 20 and the third electrode 26, respectively.
It should be noted that what is referred to as a first, a second, a
third, and a fourth electrode in the appended claims correspond to
the fourth electrode 41, the fifth electrode 42, the second
electrode 20, and the third electrode 26, respectively.
[0103] With this structure, the optical element 10 permits finer
control of the electric field distribution in the liquid crystal
layer 13, and thus acts both as a convex lens and as a concave lens
with higher accuracy.
[0104] In the second embodiment, the fourth and fifth electrodes 41
and 42 may be laid on the surface of the first transparent
substrate 11 facing toward the liquid crystal layer 13. The
exterior diameters of the fourth and fifth electrodes 41 and 42, so
long as they are each larger than the diameter of the hole in the
electrode located adjacently on the liquid crystal layer 13 side
thereof, do not necessarily have to be all equal. The fourth and
fifth electrodes 41 and 42, so long as they fulfill the conditions
stated previously in connection with the second and third
electrodes 20 and 26 of the first embodiment, do not necessarily
have to have exactly the same structures as the second and third
electrodes 20 and 26, respectively.
Third Embodiment
[0105] A third embodiment of the present invention will be
described below with reference to the relevant drawings. Such parts
as find their counterparts in the first or second embodiment will
be identified by common reference numerals, and no explanation
thereof will be repeated.
[0106] First, a description will be given of the construction of an
optical pickup to which the optical element 10 of each embodiment
is applicable.
[0107] FIG. 12 is a diagram illustrating an outline of the
construction of the optical pickup dealt with in this embodiment.
This optical pickup is provided with: light sources 61, 62, and 63;
beam splitters 64, 65, and 66; a collimator lens 67; an adjustment
lens 68; a collimator lens 69; a half-mirror 70, a quarter-wave
plate 71, a condenser lens (objective lens) 72; and photosensors 73
and 74. In this optical pickup, the optical element 10 is arranged
in the optical path between the half-mirror 70 and the quarter-wave
plate 71. The optical element 10 is designed to be capable of
correcting coma, a detailed description of which will be given
later.
[0108] The light sources 61, 62, and 63 are, for example, laser
diodes, and emit light toward an optical disc D. In this
embodiment, the light source 61 emits light of a wavelength (for
example, 785 nm) corresponding to CDs; the light source 62 emits
light of a wavelength (for example, 660 nm) corresponding to DVDs;
and the light source 63 emits light of a wavelength (for example,
405 nm) corresponding to next-generation DVDs (such as Blu-ray
discs and HD (high-definition) DVDs). Thus, it is possible to cope
with, as the optical disc D, any of a CD, a DVD, and a
next-generation DVD.
[0109] Any of the light sources 61, 62, and 63 may emit light of
any of the wavelengths corresponding to CDs, DVDs, and
next-generation DVDs. For example, the light source that emits
light of the wavelength corresponding to CDs is not limited to the
light source 61.
[0110] The beam splitters 64 and 65 reflect the light from the
light sources 61 and 62, respectively, toward the optical disc D,
and both transmit the light returning from the optical disc D. The
beam splitter 66 transmits the light from the light source 63, and
reflects the light returning from the optical disc D. The
collimator lens 67 condenses the light (a diverging beam) from the
light sources 61 and 62 to form it into a substantially parallel
beam. The adjustment lens 68, working with the collimator lens 69,
condenses the light from the light source 62 to form it into a
substantially parallel beam. The collimator lens 69 condenses the
light (a diverging beam) from the light source 63 to form it into a
substantially parallel beam. The collimator lenses 67 and 69 and
the adjustment lens 68 are driven to move by an unillustrated
driving mechanism for the purpose of varying the position at which
the light shone on the optical disc D is condensed according to the
type of the optical disc D used. The half-mirror 70 transmits the
light from the light sources 61 and 62 to direct it toward the
optical disc D, and reflects the light from the light source 63 to
direct it toward the optical disc D.
[0111] The quarter-wave plate 71 converts the light (linearly
polarized) emitted from the light sources 61, 62, and 63 into
circularly polarized light, and converts the light (circularly
polarized) returning from the optical disc D into linearly
polarized light polarized perpendicularly to the polarization
direction of the light as it entered the quarter-wave plate 71 for
the first time. The condenser lens 72 condenses the light that has
entered it on the information recording surface of the optical disc
D. The photosensors 73 and 74 sense the light returning from the
optical disc D to detect, during recording to or reproduction from
the optical disc D, servo signals (a focus error signal and a
tracking error signal), an information signal, an aberration
signal, and the like.
[0112] In the construction described above the linearly polarized
light emitted from the light source 61 is reflected from the beam
splitter 64, is then transmitted through the beam splitter 65, and
then enters the collimator lens 67, which then converts the light
into a substantially parallel beam, which is then transmitted
through the half-mirror 70, and then enters the optical element 10.
The linearly polarized light emitted from the light source 62 is
transmitted through the adjustment lens 68, is then reflected from
the beam splitter 65, and then enters the collimator lens 67. The
light from the light source 62 is converted into a substantially
parallel beam by the adjustment lens 68 and the collimator lens 67,
is then transmitted through the half-mirror 70, and then enters the
optical element 10. The linearly polarized light emitted from the
light source 63 is transmitted through the beam splitter 66, is
then converted into a substantially parallel beam by the collimator
lens 69, is then reflected from the half-mirror 70, and then enters
the optical element 10. The light that has entered the optical
element 10 then has coma aberration corrected therein, then exits
therefrom, is then converted into a circularly polarized light by
the quarter-wave plate 71, and is then condensed on the information
recording surface of the optical disc D by the condenser lens
72.
[0113] The light returning from the optical disc D passes through
the condenser lens 72, is then converted by the quarter-wave plate
71 into linearly polarized light polarized perpendicularly to the
polarization direction of the light as it entered the quarter-wave
plate 71 for the first time, then passes through the optical
element 10, and then strikes the half-mirror 70. Here, if the light
returning from the optical disc D is light of the wavelength (785
nm or 660 nm) corresponding to CDs or DVDs, the returning light is
transmitted through the half-mirror 70 as it is, is then
transmitted through the collimator lens 67 and then through the
beam splitters 65 and 64, and is sensed by the photo sensor 73,
which then converts the light into an electrical signal. If the
light returning from the optical disc D is light of the wavelength
(405 nm) corresponding next-generation DVDs, the returning light is
reflected from the half-mirror 70, is then transmitted through the
collimator lens 69, is then reflected from the beam splitter 66,
and is then sensed by the photo sensor 74, which then converts the
light into an electrical signal.
[0114] Next, a detailed description will be given of the optical
element 10. As described above, the optical element 10 of this
embodiment is applicable to a system that condenses the light from
the light sources 61, 62, and 63 on a recording medium to achieve
recording thereto or senses the light reflected from the recording
medium to read information recorded thereon. In addition, the
optical element 10 of this embodiment permits correction of coma
resulting from a warp or inclination in the recording medium. More
specifically, the optical element 10 is structured as described
below.
[0115] FIG. 13A is a plan view showing an outline of the structure
of the optical element 10 of this embodiment, and FIG. 13B is a
cross-sectional view thereof along line C-C' shown in FIG. 13A as
viewed in the arrow-indicated direction. It should be noted that,
in FIG. 13A, a second transparent substrate 12 is omitted from
illustration. The optical element 10 of this embodiment has a
liquid crystal layer 13 sandwiched between a first transparent
substrate 11 and a second transparent substrate 12.
[0116] On the liquid crystal layer 13 side of the first transparent
substrate 11, an electrode 81 is formed over the entire substrate.
On the liquid crystal layer 13 side of the second transparent
substrate 12, electrodes 82 and 83 are formed in this order from
the liquid crystal layer 13 side. The electrodes 82 and 83 are
formed of, for example, a transparent substance such as ITO (indium
tin oxide), and each form a plurality of individual electrodes. The
electrode 83 is formed on the second transparent substrate 12, and
apart from the liquid crystal layer 13 with the electrode 82 and an
insulating layer 84 laid in between. The insulating layer 84 is
formed of for example, a silicon nitride (Si.sub.3N.sub.4), silicon
oxide (SiO.sub.2), or polyimide. The electrodes 81, 82, and 83 are
connected, via conductors 31, to voltage applying means 30. The
voltage applying means 30 functions as a voltage applier that
varies the alignment of the liquid crystal molecules in the liquid
crystal layer 13 through application of voltages to the electrodes
81, 82, and 83.
[0117] The liquid crystal layer 13 is sealed in with a sealing
member 85. The electrode 82 and the insulating layer 84 are, along
with the liquid crystal layer 13, formed inside the sealing member
85, that is, within the area where the liquid crystal layer 13 is
formed. By contrast, the electrode 83 is so formed that a part
thereof protrudes out of the area where the liquid crystal layer 13
is formed and faces the sealing member 85.
[0118] As described above, the optical element 10 of this
embodiment is provided with a liquid crystal layer 13, transparent
substrates (a first transparent substrate 11 and a second
transparent substrate 12) arranged one on each side of the liquid
crystal layer 13, and electrodes (electrodes 81, 82, and 83)
arranged one or two on each side of the liquid crystal layer 13,
wherein, through application of voltages to the electrodes by
voltage applying means 30, the alignment of the liquid crystal
molecules in the liquid crystal layer 13 is varied. Moreover, the
electrodes on one side (the second transparent substrate 12 side)
of the liquid crystal layer 13 are composed of a plurality of
individual electrodes (electrodes 82 and 83) laid on each other
with an insulating layer 84 laid in between.
[0119] Next, a detailed description will be given of the electrodes
82 and 83. FIG. 14A is a plan view showing an outline of the
structure of the electrode 82. The electrode 82 is, among the
plurality of individual electrodes, the one closest to the liquid
crystal layer 13 (in the first layer from the liquid crystal layer
13 side), and is formed continuous within the optical path. That
is, the electrode 82 neither is divided into a plurality of
electrodes nor has insular electrodes within the optical path. Then
viewed from a perspective perpendicular to the liquid crystal layer
13, the electrode 82 has the outer edge thereof encircling an area
larger than the area where the light beam passes. The electrode 82
has a transparent part within the optical path. This helps avoid a
lowering of the transmissivity of the electrode 82 to the light
transmitted therethrough.
[0120] Moreover, the electrode 82 has holes 82a and 82b (first
holes), two of each, within the optical path. The holes 82a and 82b
are formed in positions corresponding to the peaks of coma. That
is, the electrode 82 is not formed where large coma occurs.
[0121] The holes 82a are longitudinally elongate, and are composed
of two holes 82a.sub.1 and 82a.sub.2. The holes 82a.sub.1 and
82a.sub.2 are arranged side by side, with the optical axis at the
center between them. On the other hand, the holes 82b are
crescent-shaped, and are composed of two holes 82b.sub.1 and
82b.sub.2. The hole 82.sub.1 is formed, with the concave part
thereof facing inward (toward the optical axis), outside the hole
82a.sub.1 (on the side thereof facing away from the optical axis).
The hole 82b.sub.2 is formed, with the concave part thereof facing
inward, outside the hole 82a.sub.2. Thus, of the two pairs of holes
82a and 82b, the holes 82a.sub.1 and 82b.sub.1 and the holes
82a.sub.2 and 82b.sub.2 are formed in positions line-symmetric, and
also point-symmetric about the optical axis, in the electrode
82.
[0122] The electrode 82 also has a part thereof protruding out of
the optical path to form a lead portion 82c. To this lead portion
82c, a conductor 31 leading to the voltage applying means 30 is
connected.
[0123] FIG. 14B is a plan view showing an outline of the structure
of the electrode 83. The electrode 83 is, among the plurality of
individual electrodes, the one farthest from the liquid crystal
layer 13, and is composed of a plurality of electrodes (electrode
segments) 83a and 83b formed in the same layer. The electrodes 83a
and 83b are each formed substantially in the shape of a ring having
a part thereof cut out, and are arranged so as to mesh with each
other without touching each other.
[0124] Moreover, the electrodes 83a and 83b are so formed as to
cover the holes 82a and 82b of the electrode 82 shown in FIG. 14A.
More specifically, the electrode 83a is formed continuous so as to
cover the holes 82a.sub.2 and 82b.sub.1 of the electrode 82, and
the electrode 83b is formed continuous so as to cover the holes
82a.sub.1 and 82b.sub.2 of the electrode 82.
[0125] Moreover, the electrodes 83a and 83b have parts thereof
protruding out of the optical path to form lead portions 83c and
83d, respectively. To these lead portions 83c and 83d, conductors
31 leading to the voltage applying means 30 are connected.
[0126] Next, a description will be given of the voltage control in
the optical element 10 structured as described above. FIG. 15 shows
the voltages applied to the different electrodes of the optical
element 10, the phase of the light (solid line P) transmitted
through the liquid crystal layer 13, and the coma observed (solid
line Q). In a case where the liquid crystal molecules of the liquid
crystal layer 13 are negatively dielectric, that is, in a case
where the value (dielectric anisotropy) calculated by subtracting
the dielectric constant observed when a voltage is applied along
the minor axis of the molecules from the dielectric constant
observed when a voltage is applied along the major axis of the
molecule is negative, when voltages V1, V2, V3, and V4 (where
V1<V3<V2<V4) are applied to the electrodes 81, 82, 83a,
and 8b, respectively, the alignment of the liquid crystal molecules
in the liquid crystal layer 13 changes to vary the refractive index
of the liquid crystal layer 13 in such a way as to produce a phase
pattern as indicated by solid line P in the transmitted light. This
phase pattern is roughly an inversion of the pattern of coma
indicated by solid line Q. Thus, through application of voltages to
the different electrodes, it is possible to vary the refractive
index of the liquid crystal layer 13 and thereby control the phase
of the transmitted light so as to correct the coma produced through
the optical system. In a case where the liquid crystal molecules of
the liquid crystal layer 13 are positively dielectric, the voltages
applied have a pattern inverted as compared with the one shown in
the figure.
[0127] As described above, in this embodiment, the electrode 82,
that is the individual electrode closest to the liquid crystal
layer 13, is formed continuous within the optical path. This makes
it possible, as in this embodiment, to form part of the electrode
82 into a lead portion 82c so that the conductor 31 connected to
the lead portion 82c is located outside the optical path. This
helps eliminate the influence of the conductor 31 on the electric
field distribution in the liquid crystal layer 13 and thereby
obtain an ideal electric field distribution in the liquid crystal
layer 13. Thus, it is possible to avoid degradation of the
characteristics of the optical element 10 attributable to the
conductor 31. Moreover, the electrode 82 is formed to have holes
82a and 82b, and thus, according to where the holes 82a and 82b are
formed, the electric field distribution can be varied to correct
coma.
[0128] In particular, in this embodiment, the holes 82a and 82b of
the electrode 82 are formed in positions corresponding to the peaks
of coma. This makes it possible to correct coma without laying, in
the optical path, conductors leading to insular electrodes formed
in such positions as conventionally practiced.
[0129] Also in the first and second embodiment described
previously, the individual electrode 21a (see FIG. 2 etc.) closest
to the liquid crystal layer 13 is formed to be continuous within
the optical path and to have a hole 27 within the optical path.
With this structure, as described previously, by controlling the
voltages applied to the different electrodes, it is possible,
without laying conductors 31 within the optical path, to give the
liquid crystal layer 13 a capability to vary the focal length to
act as a lens or a capability to correct aberration (for example,
spherical aberration).
[0130] To sum up, to eliminate the influence of conductors on the
electric field distribution and to make correction of aberration
possible, the individual electrode closest to the liquid crystal
layer needs to be formed so as to be continuous within the optical
path and to have a hole within the optical path.
[0131] Moreover, in this embodiment, the electrode 83 is so formed
as to cover the holes 82a and 82b of the electrode 82, and thus,
along the optical axis, at least one of the electrodes 82 and 83
exists. Thus, by applying voltages to the electrode 81, which is
formed over the entire surface of the first transparent substrate
11, and to the electrodes 82 and 83, it is possible, over the
entire area of the liquid crystal layer 13, to properly control the
refractive index of the liquid crystal layer 13 to control the
phase of the transmitted light.
[0132] Moreover, the electrode 83 is composed of a plurality of
electrodes (electrode segments) 83a and 83b laid in the same layer.
Thus, it is possible, as in this embodiment, to apply different
voltages V3 and V4 to the electrodes 83a and 83b. This makes it
possible, in the liquid crystal layer 13, to make different the
phase of the transmitted light between in the area where the
electrodes 83a and 81 face each other through the holes 82a and 82b
of the electrode 82 and in the area where the electrodes 83b and 81
face each other through the holes 82a and 82b of the electrode 82.
This makes it possible to correct coma properly.
Fourth Embodiment
[0133] A fourth embodiment of the present invention will be
described below with reference to the relevant drawings. Such parts
as find their counterparts in any of the first to third embodiments
will be identified by common reference numerals, and no explanation
thereof will be repeated.
[0134] FIG. 16A is a plan view showing an outline of the structure
of the optical element 10 of this embodiment and FIG. 16B is a
cross-sectional view thereof along line D-D' shown in FIG. 16A as
viewed in the arrow-indicated direction. It should be noted that,
in FIG. 16A, a second transparent substrate 12 is omitted from
illustration. The optical element 10 of this embodiment has the
same structure as that of the third embodiment except that, on the
second transparent substrate 12 side of the liquid crystal layer
13, in addition to the electrodes 82 and 83, an electrode 86 is
also arranged that is connected to a conductor 31.
[0135] The electrode 86 is, among the plurality of individual
electrodes laid on the second transparent substrate 12 side of the
liquid crystal layer 13, the individual electrode in the second
layer from the liquid crystal layer 13 side. That is, the electrode
86 is laid between the electrode 82 and the electrode 83. The
electrode 86 is formed of, for example, a transparent material such
as ITO, and is formed apart from the electrodes 82 and 83 and from
the liquid crystal layer 13 with insulating layers 84 laid in
between.
[0136] FIG. 17 is a plan view showing an outline of the structure
of the electrode 86. Like the electrode 82, the electrode 86 is
formed continuous within the optical path, and is so formed that,
when viewed from a perspective perpendicular to the liquid crystal
layer 13, the outer edge thereof encircles and area larger than the
area where the light beam passes.
[0137] Moreover, the electrode 86 has holes 86a and 86b (second
holes), two of each, within the optical path. The holes 86a and 86b
are formed in positions corresponding to the peaks of coma. That
is, the electrode 86 is not formed where large coma occurs.
[0138] The holes 86a are longitudinally elongate, and are composed
of two holes 86a.sub.1 and 86a.sub.2. The holes 86a.sub.1 and
86a.sub.2 are arranged side by side, with the optical axis at the
center between them. On the other hand, the holes 86b are
crescent-shaped, and are composed of two holes 86b.sub.1 and
86b.sub.2. The hole 86b.sub.1 is formed, with the concave part
thereof facing inward, outside the hole 86a.sub.1. The hole
86b.sub.2 is formed, with the concave part thereof facing inward,
outside the hole 86a.sub.2. Thus, of the two pairs of holes 86a and
86b, the holes 86a.sub.1 and 86b.sub.1 and the holes 86a.sub.2 and
86b.sub.2 are formed in positions line-symmetric, and also
point-symmetric about the optical axis, in the electrode 86.
[0139] The holes 86a and 86b of the electrode 86 are formed smaller
than the holes 82a and 82b of the electrode 82. More specifically,
the holes 86a.sub.1 and 86a.sub.2 are formed smaller than the holes
82a.sub.1 and 82a.sub.2, respectively, and the holes 86b.sub.1 and
86b.sub.2 are formed smaller than the holes 82b.sub.1 and
82b.sub.2, respectively. Moreover, the holes 86a and 86b of the
electrode 86 are so formed that the rims thereof lie inside the
rims of the holes 82a and 82b of the electrode 82.
[0140] The electrode 86 has a part thereof protruding out of the
optical path to form a lead portion 86c. To this lead portion 86c,
a conductor 31 leading to the voltage applying means 30 is
connected.
[0141] In this embodiment, an electrode 86 is arranged as an
individual electrode in the second layer from the liquid crystal
layer 13 side so that, through application of adequate voltages to
the different electrodes 81, 82, 86, and 83, the electric field
distribution in the liquid crystal layer 13 can be controlled more
finely than in the third embodiment. This makes it possible, as
shown in FIG. 18, to control the phase pattern of the light
transmitted through the liquid crystal layer 13 stepwise as
indicated by solid line P, and thereby to make the phase pattern
closer to a phase pattern inverted as compared with the pattern of
coma indicated by solid line Q. As a result, it is possible to
correct coma finely and hence properly.
[0142] This embodiment deals with a case where, on the second
transparent substrate 12 side of the liquid crystal layer 13, three
electrodes 82, 86, and 83 are formed, that is a plurality of
individual electrodes are formed in three layers; it is, however,
also possible to form them in four or more layers. Specifically,
let the number of layers of individual electrodes arranged on the
second transparent substrate 12 side of the liquid crystal layer 13
be n (where n is a natural number equal to or greater than 3).
Then, by forming the individual electrodes in the first to (n-1)th
layers each continuous within the optical path and having holes,
moreover forming the holes in positions corresponding to the peaks
of coma, and moreover forming the holes of, of every two adjacent
individual electrodes, the one farther from the liquid crystal
layer 13 smaller than the holes of the one closer to the liquid
crystal layer 13, it is possible to correct coma finely and hence
properly.
[0143] In a case where a plurality of individual electrodes are
laid in three or more layers, when, except the individual electrode
farthest from the liquid crystal layer 13 (that is, the individual
electrode in the nth layer from the liquid crystal layer 13 side),
the rest of the individual electrodes (that is, the individual
electrodes in the first to (n-1)th layers from the liquid crystal
layer 13 side)are each so formed as to be continuous within the
optical path and to have holes within the optical path, there is no
need to lay, within the optical path, conductors for applying
voltages to the individual electrodes. Thus, it is possible to
eliminate the influence of the conductors on the electric field
distribution. Here, when the holes of the individual electrodes
other than the one farthest from the liquid crystal layer 13 are
formed increasingly small away from the liquid crystal layer 13, it
is possible to control the electric field distribution in the
liquid crystal layer 13 finely.
Fifth Embodiment
[0144] A fifth embodiment of the present invention will be
described below with reference to the relevant drawings. Such parts
as find their counterparts in any of the first to fourth
embodiments will be identified by common reference numerals, and no
explanation thereof will be repeated.
[0145] FIG. 19A is a plan view showing an outline of the structure
of the optical element 10 of this embodiment, and FIG. 19B is a
cross-sectional view thereof along line E-E' shown in FIG. 19A as
viewed in the arrow-indicated direction. The optical element 10 of
this embodiment has the same structure as that of the third
embodiment except that a plurality of individual electrodes, namely
electrodes 82 and 83, are formed on the side of the second
transparent substrate 12 facing away from the liquid crystal layer
13. That is, in this embodiment, the electrode 82 is formed on the
surface of the second transparent substrate 12 facing away from the
liquid crystal layer 13, and the electrode 83 is formed apart from
the electrode 82 and the second transparent substrate 12 with an
insulating layer 84 laid in between.
[0146] In this structure, between the liquid crystal layer 13 and
the electrodes 82 and 83, the second transparent substrate 12,
which is a comparatively thick insulating member, is located. This
makes it possible to produce an electric field distribution
smoothly not only in the part of the liquid crystal layer 13
directly facing the electrode 82 but also over a wide area in the
liquid crystal layer 13. As a result, as indicated by solid line P
in FIG. 20, it is possible to vary the refractive index
distribution continuously over a wide area in the liquid crystal
layer 13, and thereby to correct coma, as indicated by solid line
Q, smoothly.
[0147] FIG. 21 is a cross-sectional view showing another example of
the structure of the optical element 10 of this embodiment. In this
optical element 10, a plurality of individual electrodes, namely
electrodes 82 and 83, are formed on the liquid crystal layer 13
side of the second transparent substrate 12, and in addition, not
only the electrode 83, but also the electrode 82 is formed apart
from the liquid crystal layer 13 with an insulating layer 84 laid
in between. In these respects, this example differs from the third
embodiment.
[0148] In this structure, between the liquid crystal layer 13 and
the electrodes 82 and 83, the insulating layer 84, which is a
comparatively thick insulating member, is located. Thus, as with
the optical element 10 shown in FIG. 20, it is possible to produce
an electric field distribution smoothly over a wide area in the
liquid crystal layer 13. Thus, just as described above, it is
possible to vary the refractive index distribution continuously
over a wide area in the liquid crystal layer 13, and thereby to
correct coma smoothly.
[0149] In addition, forming the insulating layer 84 between the
liquid crystal layer 13 and the electrodes 82 and 83 makes it
easier to reduce the thickness than arranging a substrate formed
of, for example, glass between the liquid crystal layer 13 and the
electrodes 82 and 83.
Sixth Embodiment
[0150] A sixth embodiment of the present invention will be
described below with reference to the relevant drawings. Such parts
as find their counterparts in any of the first to fifth embodiments
will be identified by common reference numerals, and no explanation
thereof will be repeated.
[0151] FIG. 22A is a plan view showing an outline of the structure
of the optical element 10 of this embodiment, and FIG. 22B is a
cross-sectional view thereof along line F-F' shown in FIG. 22A as
viewed in the arrow-indicated direction. In the optical element 10
of this embodiment, the electrode pattern on the first transparent
substrate 11 side of the liquid crystal layer 13 and the electrode
pattern on the second transparent substrate 12 side of the liquid
crystal layer 13 is symmetric with each other about the liquid
crystal layer 13.
[0152] In this embodiment, the electrode pattern on the second
transparent substrate 12 side of the liquid crystal layer 13 is,
for example, the same as the electrode pattern described previously
in connection with the third embodiment. Accordingly, the electrode
pattern on the first transparent substrate 11 side of the liquid
crystal layer 13 are, for example, as follows.
[0153] On the liquid crystal layer 13 side of the first transparent
substrate 11, electrodes 87 and 88 are formed in this order from
the liquid crystal layer 13 side. These electrodes 87 and 88
correspond to the electrodes 82 and 83, and are formed in the same
shapes as the electrodes 82 and 83. Accordingly, the electrode 87
has holes corresponding to the holes 82a and 82b of the electrode
82, and has a part thereof protruding to form a lead portion to
which a conductor 31 leading to the voltage applying means 30 is
connected. On the other hand, the electrode 88 is composed of
electrodes 88a and 88b corresponding to the electrodes 83a and 83b,
and has a part thereof protruding to form a lead portion to which a
conductor 31 leading to the voltage applying means 30 is connected.
The electrodes 87 and 88 are arranged symmetrically with the
electrodes 82 and 83 about the liquid crystal layer 13.
[0154] The electrode 88 is formed on the first transparent
substrate 11, and apart from the liquid crystal layer 13 with the
electrode 87 and an insulating layer 89 laid in between. The
insulating layer 89 can be formed of the same material as the
insulating layer 84. The second transparent substrate 12 side
electrodes 82 and 83 and the first transparent substrate 11 side
electrodes 87 and 88 are connected via conductors 31 to the voltage
applying means 30.
[0155] The electrode 87 and the insulating layer 89 are, along with
the liquid crystal layer 13, formed inside the sealing member 85,
that is, within the area where the liquid crystal layer 13 is
formed. By contrast, the electrode 88 is so formed that a part
thereof protrudes out of the area where the liquid crystal layer 13
is formed and faces the sealing member 85.
[0156] With the structure of this embodiment, the potential
difference between the first transparent substrate 11 side
electrodes and the second transparent substrate 12 side electrodes
can be made twice as large as in the third embodiment, and thus the
phase of the light transmitted through the liquid crystal layer 13
can be varied in a range twice as wide. Thus, it is possible to
correct large coma easily. On the other hand, in a case where the
variation of the phase of the transmitted light is equal to that in
the third embodiment, the voltage applied between the first
transparent substrate 11 side electrodes and the second transparent
substrate 12 side electrodes can be reduced to half as high as in
the third embodiment.
Seventh Embodiment
[0157] A seventh embodiment of the present invention will be
described below with reference to the relevant drawings. Such parts
as find their counterparts in any of the first to sixth embodiments
will be identified by common reference numerals, and no explanation
thereof will be repeated.
[0158] FIG. 23A is a plan view showing an outline of the structure
of the optical element 10 of this embodiment, and FIG. 23B is a
cross-sectional view thereof along line G-G' shown in FIG. 23A as
viewed in the arrow-indicated direction. It should be noted that,
in FIG. 23A, a second transparent substrate 12 is omitted from
illustration. The optical element 10 of this embodiment is built as
a combination of the third and first embodiments. Superficially, in
the optical element 10 of this embodiment, the electrode pattern on
the second transparent substrate 12 side of the liquid crystal
layer 13 is the same as in the third embodiment, and the electrode
pattern on the first transparent substrate 11 side of the liquid
crystal layer 13 is the same as in the first embodiment.
[0159] Described in detail, the electrode pattern on the first
transparent substrate 11 side of the liquid crystal layer 13 is as
follows. On the first transparent substrate 11 side of the liquid
crystal layer 13, an electrode 20 is arranged, which is composed of
a plurality of individual electrodes 21a to 21e that are laid on
one another with insulating layers 28 laid in between and that have
holes 27. Here, the individual electrode 21a is arranged closest to
the liquid crystal layer 13. When viewed from a perspective
perpendicular to the liquid crystal layer 13, the holes 27 of the
individual electrodes 21a to 21e are so formed that their rims do
not overlap one another, that they are increasingly small away from
the liquid crystal layer 13, and that they describe concentric
circles.
[0160] With this structure, by controlling the voltages applied to
the electrodes 82 and 83 and to the individual electrodes 21a to
21e and thereby varying the refractive index of the liquid crystal
layer 13, it is possible to obtain a capability to correct coma and
in addition a capability to correct spherical aberration and also a
capability to act as a lens (by varying the focal length). That is,
with a single optical element 10, it is possible to correct both
coma and spherical aberration. Moreover, by providing a plurality
of individual electrodes 21a to 21e, it is possible to widen the
range in which the focal length can be varied.
[0161] Moreover, as shown in FIG. 23B, by giving, of every two
adjacent individual electrodes (for example, the individual
electrodes 21a and 21b) with the insulating layer 28 laid in
between, the one farther from the liquid crystal layer 13 (for
example the individual electrode 21b) an exterior diameter larger
than the diameter of the hole of the one closer to the liquid
crystal layer 13 (for example the individual electrode 21a), it is
possible to arrange the conductors 31 for applying voltages to the
individual electrodes outside the area in which the electric field
distribution is produced. That is, the conductors 31 can be
arranged so as not to directly face the liquid crystal layer 13.
This helps avoid the influence of the conductors 31 on the electric
field distribution.
Eighth Embodiment
[0162] An eighth embodiment of the present invention will be
described below with reference to the relevant drawings. Such parts
as find their counterparts in any of the first to seventh
embodiments will be identified by common reference numerals, and no
explanation thereof will be repeated.
[0163] FIG. 24A is a plan view showing an outline of the structure
of the optical element 10 of this embodiment, and FIG. 24B is a
cross-sectional view thereof along line H-H' shown in FIG. 24A as
viewed in the arrow-indicated direction. The optical element 10 of
this embodiment has the same structure as that of the fifth
embodiment except that the electrode 83, which is located farthest
from the liquid crystal layer 13, is composed of as many electrodes
as the holes 82a and 82b of the electrode 82, which is the
individual electrode adjacent to the electrode 83. Specifically,
since the holes 82a and 82b of the electrode 82 are composed of
four holes 82a.sub.1, 82a.sub.2, 82b.sub.1, and 82b.sub.2, the
electrode 83 is composed of four electrodes 83p, 83q, 83r, and
83s.
[0164] FIG. 25 is a plan view showing an outline of the structure
of the electrode 83 in this embodiment. The electrodes 83p, 83q,
83r, and 83s are so formed as to cover the holes 82a.sub.1,
82a.sub.2, 82b.sub.1, and 82b.sub.2, respectively, of the electrode
82. Moreover, the electrodes 83p and 83r and the electrodes 83q and
83s are formed in substantially line-symmetric shapes, except in
lead portions 83p.sub.1, 83r.sub.1, 83q.sub.1, and 83s.sub.1
thereof described later.
[0165] The electrodes 83p and 83s may be regarded as the electrode
83b of the fifth embodiment as divided in two, and the electrodes
83q and 83r as the electrode 83a of the fifth embodiment as divided
in two.
[0166] The electrodes 83p, 83q, 83r, and 83s have parts thereof
protruding out of the optical path to form lead portions 83p.sub.1,
83q.sub.1, 83r.sub.1, and 83s.sub.1, respectively. To these lead
portions 83p.sub.1, 83q.sub.1, 83r.sub.1, and 83s.sub.1, conductors
31 leading to the voltage applying means 30 are connected.
[0167] FIG. 26 shows the phase (solid line P) of the light
transmitted through the liquid crystal layer 13 of the optical
element 10 of this embodiment and the coma observed (solid line Q).
In this embodiment, the electrode 83 farthest from the liquid
crystal layer 13 is composed of as many electrodes 83p, 83q, 83r,
and 83s as the total number of holes 82a and 82b in the electrode
82, which is an individual electrode in another layer. This helps
increase the flexibility with which voltages can be controlled when
correcting coma, and thus helps increase the flexibility with which
the phase of the light transmitted through the liquid crystal layer
13 can be controlled.
[0168] That is, it is possible to control the voltages applied to
the electrode 83 independently (hence finely) for each of the
electrodes 83p, 83q, 83r, and 83s corresponding to the holes
82a.sub.1, 82a.sub.2, 82b.sub.1, and 82b.sub.2 of the electrode 82.
This makes it possible, in the liquid crystal layer 13, to make
greatly different the electric field distribution between in the
area where the electrodes 81 and 83p face each other through the
hole 82a.sub.1 and in the area where the electrodes 81 and 83s face
each other through the hole 82b.sub.2, and thus to give the light
transmitted through the liquid crystal layer 13 a large phase
difference between those areas. This makes it possible to control
the phase of the transmitted light flexibly according to the coma
actually observed, and thus to achieve proper correction according
to the coma actually observed.
[0169] In FIG. 5, which shows the first embodiment described
earlier, the second electrode 20 and the unillustrated liquid
crystal layer (in particular, the part thereof surrounded with the
sealing member) are assumed to have a circular exterior shape;
instead, as shown in FIG. 27, these may have a rectangular or any
other shape. Conversely, in the other embodiments, the electrodes
and the liquid crystal layer that are assumed to have a rectangular
exterior shape may instead have a circular or any other shape.
[0170] It should be understood that all the figures that have been
referred to in the course of the description hereinbefore are
merely schematic diagrams, and therefore that, in those figures,
the dimensions of transparent substrates, electrodes, liquid
crystal layers, insulating layers, etc. are shown on different
scales in different directions and thus do not reflect actual
proportions. Needless to say, the structures of different
embodiments may be combined together.
[0171] Optical elements according to the present invention can be
used as convex lenses, concave lenses, diffraction gratings,
aberration correcting elements, and the like, and find application
in optical pickups.
[0172] As described above, according to one aspect of the present
invention, an optical element is provided with: a liquid crystal
layer; a first transparent substrate arranged on one side of the
liquid crystal layer; a first electrode transparent and arranged on
the one side of the liquid crystal layer; a second transparent
substrate arranged on the other side of the liquid crystal layer; a
second electrode arranged on the other side of the liquid crystal
layer and including a plurality of individual electrodes having
holes; a third electrode arranged on the side of the second
electrode facing away from the liquid crystal layer; an insulating
layer laid between the individual electrodes and the third
electrode; and a voltage applier for applying voltages between the
first electrode and the second and third electrodes. Here, the
holes of the individual electrodes are increasingly small away from
the liquid crystal layer.
[0173] According to another aspect of the present invention, an
optical element is provided with: a liquid crystal layer; a first
transparent substrate arranged on one side of the liquid crystal
layer; a first electrode transparent and arranged on the one side
of the liquid crystal layer; a second transparent substrate
arranged on the other side of the liquid crystal layer; a second
electrode arranged on the other side of the liquid crystal layer
and including one or more individual electrodes having holes; a
third electrode arranged on the side of the second electrode facing
away from the liquid crystal layer; an insulating layer arranged
between the individual electrodes and the third electrode; and a
voltage applier for applying voltages between the first electrode
and the second and third electrodes. Here, of the individual
electrodes of the second electrode, the one closest to the liquid
crystal layer has a transparent part within the optical path, and
is so formed as to be continuous within the optical path and to
have a hole within the optical path.
[0174] In the optical elements described above, it is preferable
that the second electrode include two or more of the individual
electrodes, and that the holes of the individual electrodes be
increasingly small away from the liquid crystal layer. This helps
widen the range in which the focal length can be varied, and helps
control the electric field distribution finely.
[0175] According to the present invention, it is preferable that,
when viewed from a perspective perpendicular to the liquid crystal
layer, the rims of the holes of the individual electrodes not
overlap one another, that the exterior diameter of each of the
individual electrodes except the one closest to the liquid crystal
layer be larger than the diameter of the hole of the individual
electrode located adjacently on the liquid crystal layer side
thereof, and that the exterior diameter of the third electrode be
larger than the diameter of the hole of the individual electrode
located adjacent thereto.
[0176] Since the exterior diameter of each individual electrode is
larger than the diameter of the hole of the individual electrode
located adjacently on the liquid crystal layer side thereof, as
viewed from a perspective perpendicular to the liquid crystal
layer, no gap is left between the individual electrodes, and thus
the conductors to the individual electrodes do not directly face
the first electrode. Thus, the conductors do not influence the
electric field produced when voltages are applied between the first
electrode and the second and third electrodes.
[0177] According to the present invention, the second electrode may
include transparent individual electrodes and non-transparent
individual electrodes. A non-transparent individual electrode acts
as an aperture stop. Thus, by making some of the individual
electrodes of the second electrode non-transparent, it is possible
to reduce the spherical aberration produced by the optical element
acting as a lens.
[0178] According to the present invention, the third electrode may
have a hole of which the diameter is smaller than the diameter of,
of the holes of the individual electrodes, the smallest one. Here,
when viewed from a perspective perpendicular to the liquid crystal
layer, the rim of the hole of the third electrode may not overlap
any of the rims of the holes of the second electrode. Forming a
hole in the third electrode in this way helps further widen the
range in which the focal length can be varied.
[0179] According to the present invention, the third electrode may
be non-transparent. Making the third electrode having a hole
non-transparent permits the third electrode to act as an aperture
stop. This helps reduce the spherical aberration produced by the
optical element acting as a lens.
[0180] According to the present invention, it is preferable that,
when viewed from a perspective perpendicular to the liquid crystal
layer, the holes of the individual electrodes of the second
electrode and the hole of the third electrode describe concentric
circles. By making the holes of the second electrode and the hole
of the third electrode concentric, it is possible to make the
electric field distribution, and hence the refractive index
distribution of the liquid crystal, axisymmetric about the center
axis through the holes. This helps enhance the accuracy with which
the optical element acts as a lens.
[0181] According to the present invention, the third electrode may
be transparent and holeless. This makes the positioning of the
third electrode easy during the fabrication of the optical element,
and thus helps enhance fabrication efficiency.
[0182] According to the present invention, the second transparent
substrate may be arranged between the liquid crystal layer and the
second electrode. By arranging the second transparent substrate
between the second electrode and the liquid crystal layer and
thereby increasing the interval between the first electrode and the
second and third electrodes, it is possible, even in a case where
the holes in the second and third electrode are large, to vary the
electric field distribution over a wide area in the liquid crystal
layer. This makes it possible to vary the refractive index of the
liquid crystal layer over an accordingly wide area, and thus to
widen the range in which the focal length can be varied.
[0183] In the optical element according to the present invention,
part thereof may be carved out, starting from near the outer edge
of the top surface of the third electrode, so as to expose part of
each of the individual electrodes of the second electrode. That is,
the optical element according to the present invention may further
have a carved-out portion where part thereof is carved out along
the optical axis, starting from near the outer edge of the top
surface of the third electrode, so as to expose part of each of the
individual electrodes of the second electrode, so that, through
this carved-out portion, part of the top surface of each individual
electrode is exposed.
[0184] Forming a carved-out portion starting from near the outer
edge of the top surface of the third electrode so as to expose part
of each individual electrode permits the exposed parts of the
individual electrodes to be used as contacts at which conductors
are easily fitted to the individual electrodes. This helps enhance
the fabrication efficiency of products incorporating the optical
elements.
[0185] According to the present invention, the second transparent
substrate may be arranged on the side of the third electrode facing
away from the liquid crystal layer. By arranging the second
transparent substrate on the side of the third electrode facing
away from the liquid crystal layer, that is, by arranging it in the
outermost layer, and thereby reducing the interval between the
first electrode and the second and third electrodes, it is possible
to make the electric force lines produced between these electrodes
perpendicular thereto and substantially parallel to one another.
This makes it possible to produce a clear pattern such as a Fresnel
zone pattern in the liquid crystal layer, and thereby to make the
optical element according to the present invention act not only as
a lens but also as an optical element that is used to correct
aberrations in an optical pickup for DVDs and the like.
[0186] According to the present invention, the voltage applier may
apply the voltages between the first electrode and the second and
third electrodes such that the potential at the third electrode is
equal to or lower than the potential at the second electrode. This
permits the optical element to act as a convex lens.
[0187] According to the present invention, the voltage applier may
apply the voltages between the first electrode and the second and
third electrodes such that the potential at the third electrode is
higher than the potential at the second electrode. This permits the
optical element to act as a concave lens.
[0188] According to another aspect of the present invention, an
optical element is provided with: a liquid crystal layer; a first
transparent substrate arranged on one side of the liquid crystal
layer; a first electrode arranged on the one side of the liquid
crystal layer and including a plurality of individual electrodes
having holes; a second electrode arranged on the side of the first
electrode facing away from the liquid crystal layer; a first
insulating layer for insulating the individual electrodes of the
first electrode from the second electrode; a second transparent
substrate arranged on the other side of the liquid crystal layer; a
third electrode arranged on the other side of the liquid crystal
layer and including a plurality of individual electrodes having
holes; a fourth electrode arranged on the side of the third
electrode facing away from the liquid crystal layer; a second
insulating layer for insulating the individual electrodes of the
third electrode from the fourth electrode; and a voltage applier
for applying voltages between the first and second electrodes and
the third and fourth electrodes. Here, the holes of the individual
electrodes of the first electrode are increasingly small away from
the liquid crystal layer, and the holes of the individual
electrodes of the third electrode are increasingly small away from
the liquid crystal layer.
[0189] In the optical element described above, the first and second
transparent substrates may each be a flat plate. Building the first
and second transparent substrates as inexpensive flat plates in
this way makes it possible to fabricate the optical element
inexpensively.
[0190] According to another aspect of the present invention, an
optical element is provided with: a liquid crystal layer;
transparent substrates arranged one on each side of the liquid
crystal layer; electrodes arranged one on each side of the liquid
crystal layer; and a voltage applier for applying voltages to the
electrodes to vary the alignment of the liquid crystal molecules in
the liquid crystal layer. Here, the electrode arranged on one side
of the liquid crystal layer is composed of a plurality of
individual electrodes that are laid on one another with an
insulating layer laid in between, and, of the individual
electrodes, the one closest to the liquid crystal layer has a
transparent part within the optical path, and is so formed as to be
continuous within the optical path and to have a hole within the
optical path.
[0191] According to the present invention, the individual
electrodes may be laid in three or more layers. Here, of the
individual electrodes, those other than the one farthest from the
liquid crystal layer may be so formed as to be continuous within
the optical path and to have holes within the optical path, and the
holes of these other individual electrodes may be formed
increasingly small away from the liquid crystal layer.
[0192] When the individual electrodes are laid in three or more
layers, and, of the individual electrodes, those other than the one
farthest from the liquid crystal layer are so formed as to be
continuous within the optical path and to have holes within the
optical path, there is no need to lay, within the optical path,
conductors for applying voltages to the individual electrodes, and
thus it is possible to eliminate the influence of the conductors on
the electric field distribution. When the holes of these other
individual electrodes are formed increasingly small away from the
liquid crystal layer, it is possible to control the electric field
distribution finely.
[0193] According to the present invention, the hole of the
individual electrode closest to the liquid crystal layer may be
formed in a position corresponding to a peak of coma. That is, the
individual electrode closest to the liquid crystal layer may
include a hole formed in a position corresponding to a peak of
coma. This permits the electric field in the liquid crystal layer
to be so produced as to correct coma.
[0194] According to the present invention, the individual
electrodes may be laid in three or more layers. In this case, of
the individual electrodes, the one in the second layer away from
the liquid crystal layer may be formed as to be continuous within
the optical path and to have a hole within the optical path, the
hole of the individual electrode in the second layer away from the
liquid crystal layer may be formed in a position corresponding to a
peak of coma, and the hole of the individual electrode in the
second layer away from the liquid crystal layer may be formed
smaller than the hole of the individual electrode closest to the
liquid crystal layer.
[0195] When the individual electrode in the second layer away from
the liquid crystal layer is so formed as to be continuous within
the optical path and to have a hole within the optical path, for
the same reason as noted previously, it is possible to avoid
degradation of the characteristics of the optical element
attributable to conductors, and it is also possible to vary the
electric field distribution according to where the hole is formed
so as to correct various aberrations.
[0196] Furthermore, when the above-mentioned individual electrode
includes a hole formed in a position corresponding to a peak of
coma, it is possible to produce the electric field distribution in
the liquid crystal layer in a way that corrects coma. Here, when
the hole of the individual electrode in the second layer away from
the liquid crystal layer is formed smaller than the hole of the
individual electrode closest to the liquid crystal layer, it is
possible to control the electric field distribution finely, and
thus to correct coma finely.
[0197] According to the present invention, of the individual
electrodes, the one farthest from the liquid crystal layer may be
so formed as to cover the holes of the other individual electrodes.
In this structure, at least one individual electrode always exists
along the optical axis. That is, when viewed from a perspective
perpendicular to the liquid crystal layer, any gap (hole) between
individual electrodes in the same layer is filled by another
individual electrode (the individual electrode farthest from the
liquid crystal layer), so that the individual electrodes cover the
entire area of the liquid crystal layer with no gap. This makes it
possible to control the refractive index of the liquid crystal
layer over the entire area thereof.
[0198] According to the present invention, the individual electrode
farthest from the liquid crystal layer may be composed of a
plurality of electrode segments laid in the same layer. This makes
it possible to apply different voltage to the different electrode
segments. Thus, the phase of the light transmitted through the area
of the liquid crystal layer corresponding one electrode segment can
be made to lead or delay relative to the phase of the light
transmitted through the area of the liquid crystal layer
corresponding another electrode segment. This makes it possible to
correct coma properly.
[0199] In the structure described above, the individual electrode
farthest from the liquid crystal layer may be composed of as many
electrode segments as there are holes in the individual electrode
adjacent thereto. This makes it possible to control the applied
voltages independently for each of the electrode segments
corresponding to the different holes of the adjacent individual
electrode. This helps increase the flexibility with which voltages
can be controlled when correcting coma, and thus helps increase the
flexibility with which the phase of the light transmitted through
the liquid crystal layer can be controlled. As a result, it is
possible to achieve proper correction according to the coma
actually observed.
[0200] According to the present invention, the electrode segments
may include one to which, despite in the same layer as the other
electrode segments, a voltage different from the voltage applied to
the other electrode segments is applied. This makes it possible to
correct coma properly.
[0201] According to the present invention, the individual
electrodes may be formed on the side of the previously-mentioned
one of the transparent substrates facing away from the liquid
crystal layer. In this case, between the liquid crystal layer and
the individual electrodes, one of the transparent substrates is
located. This makes it possible to produce an electric field
distribution not only in the area of the liquid crystal layer
directly facing the individual electrodes but over a wide area of
the liquid crystal layer. That is, it is possible, over a wide area
of the liquid crystal layer, to form a refractive index
distribution smoothly and make it vary continuously. This makes
smooth aberration correction possible.
[0202] According to the present invention, the individual
electrodes may be formed on the side of the one of the transparent
substrates facing toward the liquid crystal layer, with an
insulating layer laid between the individual electrodes and the
liquid crystal layer.
[0203] In this structure, between the liquid crystal layer and the
individual electrodes, an insulating layer is formed. This makes it
possible to produce an electric field distribution not only in the
area of the liquid crystal layer directly facing the individual
electrodes but over a wide area of the liquid crystal layer. That
is, it is possible, over a wide area of the liquid crystal layer,
to form a refractive index distribution smoothly and make it vary
continuously. This makes smooth aberration correction possible.
[0204] According to the present invention, the electrode pattern on
the other side of the liquid crystal layer and the electrode
pattern on the one side of the liquid crystal layer may be
symmetric with each other about the liquid crystal layer.
[0205] This makes it possible to make the potential difference
between the electrode on the side of one transparent substrate and
the electrode on the side of the other transparent electrode twice
as large as when an electrode is formed only in one layer, for
example, on the side of the other transparent substrate, and thus
to make the variation of the phase of the transmitted light twice
as large. On the other hand, in a case where the variation of the
phase of the transmitted light is not varied, it is possible to
make the voltages applied to the electrode on the side of one
transparent substrate and the electrode on the side of the other
transparent electrode half as high.
[0206] According to the present invention, the electrode on the
other side of the liquid crystal layer may be composed of a
plurality of individual electrodes that are laid on one another
with an insulating layer laid in between and that have holes, and
the holes of the individual electrodes may be formed increasingly
small away from the liquid crystal layer so that, when viewed from
a perspective perpendicular to the liquid crystal layer, the rims
of the holes of the individual electrodes do not overlap one
another.
[0207] In this case, by controlling the voltages applied to the
individual electrodes and thereby varying the refractive index of
the liquid crystal layer, it is possible, more effectively, to
obtain a capability to correct spherical aberration and a
capability to act as a lens while varying the focal length
thereof.
[0208] In the structure described above, of every two of the
individual electrodes adjacent to each other across the insulating
layer laid in between, the one farther from the liquid crystal
layer may have a larger exterior diameter than the diameter of the
hole of the one closer to the liquid crystal layer. This makes it
possible to lay the conductors for applying voltages to the
individual electrodes outside the area where the electric field
distribution is produced. This helps avoid the influence of the
conductors on the electric field distribution.
[0209] Obviously, many modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims, the invention may be practiced other than as specifically
described.
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